Alkyl esters of sulphato-carboxylic acids



Patented 24, 1940 PATENT OFFICE 7 2,225,673 ALKYL ESTERS orSULPHATO-C'ARBOXYLIC ACIDS James Herbert Werntz, :Brandywine Hundred,DeL, assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., acorporation of Delaware No Drawing. Application June 16, 1939, SerialNo. 279,389

10 Claims.

This invention relates to new chemical compounds, their methods ofmanufacture, and their technical uses, and more particularly to theproduction and utilization of alkyl esters of branched-chain, aliphaticmono-sulphato-monocarboxylic acids wherein the alkyl radical contains atleast 4 carbon atoms and the monocarboxylic acid radical contains atleast 4 carbon atoms.

This invention has as an object the preparation of a number of newchemical compounds which have surface active properties. A furtherobject is to manufacture these new compounds by novel and easilyconducted processes which give high yields of products of relativelyhigh quality. 'A still further object is to use these new compounds invarious technical processes wherein surface active compounds arecommonly employed. Other objects will appearhereinafter.

These objects are accomplished by the following invention which relatesin a general way to the production of alkyl esters of branched-chain,aliphatic mono-sulphato-monocarboxylic acids wherein the alkyl radicalcontains carbon atomspreferably from 6 to 16 carbon atoms-and themonocarboxylic acid radical con- .tains at least 4 carbonatoms-preferably from 6 to 12 carbon atoms. In the preferred embodimentsof this invention the alkyl radicals of these esters are derived frombranched, open chain alcohols, and the sulphato group is attached to thecarbon atom in the monocarboxylic acid radical which is in alphaposition to the carboxyl group. These alkyl esters of branched-chainaliphatic sulphato-mono'carboxylic acids may be made by sulphating alkylesters of monohydroxy or mono-unsaturated, branched-chain, aliphaticmonocarboxylic acids. The products of this invention may also beobtained by esterifying a branched chain aliphatic sulphatomonocarboxylic acid with an aliphatic alcohol.

The following examples illustrate but do not limit the invention. Allparts are given by Weight.

EXAMPLE I alpha-(sodium sulphate) -betaethyl-heptoate Beta-ethylhexyl atleast 4.

filtered and the ether evaporated. The soft, :1

viscous, yellow oil, after drying over phosphorus pentoxide in a vacuumdesiccator, amounted to 14 parts. The product, beta-ethylhexyl alpha-(sodium sulphato)-beta-ethylheptoate, formed foaming aqueous solutionswhich wet powdered sulphur. Dilute aqueous solutions of this product wetskeins of cotton thread very rapidly when tested by the method of Dravesand Clarkson (American Dyestuffs Reporter 20, 201 (1931)).

EXAMPLE II Octyl alpha-(sodium sulphato)-beta-ethylvalerate Twenty-fiveand eight-tenths parts of n-octyl alpha-hydroxy-beta-ethylvalerate wasdissolved in '72 parts of anhydrous ethyl ether and cooled to 0 0.Twelve and eight-tenths parts of chlorosulphonic acid was slowly addedto the reaction mixture which was then stirred for 3 hours. Two

wasisolated as a viscous white syrup (36.5 parts).

Dilute aqueous solutions of n-octyl alpha-(sodiumsulphato)-beta-ethylvalerate wet powdered sulphur rapidly and are verygood wetting agents for cotton thread when tested by the method ofDraves and Clarkson. On an equal active ingredient basis this productwith the straightchain octyl group is somewhat inferior as a wettingagent to the product of Example I which has the branched-chain2-ethylhexyl group.

EXAMPLE III Dodecyl alpha- (sodium sulphate) Jada-ethylvalerateTwenty-five and two-tenths parts of n-dodecylalpha-hydroxy-beta-ethyl-valerate was dissolved in 72 parts of anhydrousethyl ether and sulphated with 11.6 parts of chloro-sulphonic acid at 0C. After stirring 3 hours, ice was added to the reaction mixture, whichwas then neutralized with 4% sodium hydroxide solution. The reactionmixture was extracted with ethyl ether and the ether extracts dried withsodium sulphate, filtered and the ether evaporated. After drying overphosphorus pentoxide in a vacuum desiccator, 35 parts of a white viscoussyrup was obtained which analyzed 7.6% sulphur. The theoretical sulphurcontent of dodecyl alpha- (sodium sulphato)-beta-ethylvalerate is 7.5%.The product gives foaming solutions in water which wet powdered sulphur.Dilute aqueous solutions of the product are very good wetting agents forcotton thread when tested by the method of Draves and Clarkson.

EXAMPLE IV A mixture of alkyl esters is prepared by esterifying amixture of acids comprising alphahydroxy isovaleric acid,alpha-hydroxy-betaethyl-Valerie acid and alpha-hydroxy-beta-ethylheptoicacid with a fraction boiling from 180- 200 C. of the mixture of higheraliphatic alcohols obtained in the catalytic synthesis of methanol fromcarbon monoxide and hydrogen. This fraction of these alcohols containssome 4- or 5- methyl heptanol-l and various unidentified primary andsecondary branched, open-chain alcohols of higher carbon content.Fifteen parts of this mixture of esters is dissolved in 85 parts ofethyl acetate and sulphated at 10 to 20 C.

by adding 7 parts of chlorosulphonic acid. The mixture of sulphatedesters is neutralized with an aqueous solution of sodium hydroxide andthe product is isolated and purified as described in Example I.

It is to be understood that the aforementioned examples are illustrativemerely of the many modifications of the present invention. Theindividual components, the proportion of such components and conditionsfor reacting them may vary Widely Without departing from the scope ofthe invention. The products contain not more than one sulphate group onthe residue of the acid, since it has been observed that more than onesulphate group tends to disturb the balance between the lipophile andthe hydrophile portions of the molecule and renders the products lessefficient, especially when they are to be employed as wetting agents.

The esters to be sulphated may be prepared from branched or straight,open-chain, saturated aliphatic alcohols containing at least 4 carbonatoms, such as the straight and branched-chain primary and the variousisomeric secondary butyl alcohols, amyl alcohols, hexyl alcohols, heptylalcohols, octyl alcohols, nonyl alcohols, decyl alcohols, undecylalcohols, dodecyl alcohols, tridecyl alcohols, tetradecyl alcohols,pentadecyl alcohols, hexadecyl alcohols, octadecyl alcohols, etc.

These alcohols may be obtained by the hydrogenation of acids or estersof animal, vegetable or synthetic origin, or by the chemical orcatalytic reduction of aldehydes or ketones. A few of the alcohols whichcan be used in preparing the esters to be sulphated are isobutylalcohol, hexanol-l, 2-ethylbutanol, heptanol-l, 2,4-dimethylpentanol-l,2,4-dimethylhexanol-3, octa nol-3, octanol-Z, 5-ethylheptanol-2,decanol-l, 5- ethylnonanol-2, 3-ethyldecanol-6, 3-ethylundecanol-6,tridecanol-2, tetradecanol-l, pentadecanol-8, 3,9-diethylundecanol-6,hexadecanol-l, octadecanol-l, 4,6 dimethylheptanol 1,2,4,6trimethyloctanol-l, 2,4,6,8-tetramethyldecanol-1, 7-ethyl-2-methylundecanol-4, the branched-chain alcohols obtained in thecatalytic synthesis of methanol by the hydrogenation of carbon monoxide,etc. In place of individual alcohols, mixtures thereof may be used, thevarious components of which may vary fromtraces to major fractions. Ingeneral I prefer to use primary alcohols and especially branched-chainprimary alcohols of which Z-ethylhexanol-l is the preferred example.

In selecting monocarboxylic branched-chain aliphatic acids foresterification, it should be understood that the acids should containeither one double bond or one hydroxyl group. The esterifyin-g acidcontaining a double bond or a hydroxyl group may be subjected totreatment with sulphating agents either prior to, simultaneously with,or preferably subsequent to the esterification reaction. Suitablealpha-hydroxy-branchedchain monocarboxylic acids are readily obtained byreacting branched-chain aldehydes or ketones,

such as isobutyraldehyde, Z-ethylbutyraldehyde, Z-ethylhexaldehyde,diisopropyl ketone, etc. with hydrogen cyanide and then hydrolyzing theresulting hydroxynitrile. A few examples of suitable acids includealpha-hydroxyisobutyric acid, alpha-hydroxyisovaleric acid,alpha-hydroxy-alpha-methylbutyric acid, alpha-hydroxy-gammamethylvalericacid, alpha-hydroxy-alpha-ethylbutyric acid,alpha-hydroxy-alpha-methyl-betamethylbutyric acid,alpha-hydroxy-beta-methylbutyric acid, alpha-hydroxy-alpha-propylvalericacid, acid, beta-hydroxy-beta-ethylvaleric acid, alphamethyl-beta-hydroxybutyric acid, beta-hydroxybeta-methylbutyric acid,alpha-ethyl-beta-hydroxypropionic acid, alpha dimethyl betahydroxypropionic acid, alpha-ethyl-beta-hydroxybutyric acid,alpha-methyl-beta-hydroxyvaleric acid, beta-hydroxyisocaproic acid,beta-hydroxyisoheptylic acid, etc.

The gamma, delta and epsilon hydroxy branched-chain monocarboxylic acidsrepresent another class of hydroxyacids which may be employed foresterification. These hydroxy acids are usually isolated as lactones. ofthis class are alpha-ethyl-gamma-hydroxybutyric acid,beta-methyl-gamma-hydroxyvalerio acid, gamma-methyl-gamma-hydroxyvalericacid, delta-methyl-gamma-hydroxycaprcic acid, alpha,alpha-dimethyl-gamma-hydroxy-valeric acid,alpha-ethyl-gamma-hydroxyvaleric acid, alpha,alpha-dimethyl-delta-hydroxyvaleric acid,gammaethyl-delta-hydroxycaproic acid, beta-methylepsilon-isopropylepsilon hydroxycaproic acid, etc.

A few examples of branched-chain unsaturated mono-carboxylic acids whichmay be used for esterification are methacrylic acid, alpha,beta-dimethylacrylic acid, alpha-methylcrotonic acid, alpha-ethylacrylicacid, alpha ethyl crotonic acid, alpha-ethylhexenoic acid, etc.saturated branched-chain monocarboxylic acids may also be obtained bythe removal of water from many of the above-listed hydroxymonocarboxylic acids.

In place of individual hydroxy monocarboxylic acids or unsaturatedmonocarboxylic acids, mixtures thereof may be used, the variouscomponents of which may vary from traces to major fractions.

The methods of esterifying an acid or acid derivative with an alcohol oralcohol derivative are well known, and need not be described in detailherein. However, mention may be made of the fact that suchesterification reactions may be carried out in the presence or absenceof solvents, diluents, and/or agents having an avidity for water.

I prefer to employ esters containing from 12 to 22 carbon atoms madefrom branched-chain acids containing from 6 to 12 carbon atoms withalcohols having from 6 to 16 carbon atoms. In general I prefer to usethe branched-chain alcohols for esterification.

The sulphated products described herein are true sulphuric acid esters,wherein the sulphur alpha hydroxy alpha methylundecylic' A few examplesSuitable unatom is connected to the hydrocarbon radical "hrough anoxygen atom. Sulphating agents which may be used in obtaining theproducts of this invention include concentrated sulphuric acid, fumingsulphuric acid, chlorosulphonic acid, sodium chlorosulphonate, ureasulphuric acid, S03 in ether solution, pyridine sulphuric anhydride,pyridine sodium pyrosulphate, etc. Sulvents or diluents such as water,aliphatic hydrocarbons, esters, ethers, carbon tetrachloride, tri-.chloroethylene, symmetrical dichloroethyl ether, "acetic anhydride,nitrobenzene, etc. Ethyl ether, propyl acetate and ethyl acetate arepreferred solvents for carrying out the reaction. This reaction isadvisedly carried out within the temperature range of from 30 C. to 50C. and i preferably at the lower range of temperature. 11 Esters ofhydroxy monocarboxylic acids arepreferably sulphated withchlorosulphonic acid in a suitable diluent like ethyl ether, whileesters of unsaturated monocarboxylic acids may be sulphated withsulphuric acid, sodium acid sulphate or sodium pyrosulphate or mixturesof these sulphating agents.

The sulphuric acid esters described herein may be used as such, butgenerally they are con- -.verted to their alkali metal salts byneutralization with an alkali metal hydroxide such as sodium hydroxide.The potassium, ammonium, calcium and magnesium salts may also be prearedand used. Suitable salts of the sulphuric acid esters described hereinmay also be made from such amines as dimethylamine, ethylamine, 1-diethanolamine, triethanolamine, butylamine, "1 glucamine,methylglucamine, pyridine, piperidine, cyclohexylamine, aniline,toluidine, etc.

The term esters of branched-chain sulphatomonocarboxylic acids as usedin the description and claims is to be understood to refer generical- 1yto the sulphated esters comprehended by the I present invention,irrespective of whether or how the sulphated esters may be neutralized.1 It has been observed in a study of a homologous series ofsurface-active agents that the more efficient products are frequently ofsuch a high molecular weight as to have too poor solubility in aqueoussolutions for satisfactory commercial application. It has now been notedthat esters of sulphated branched-chain monocarboxylic acids have agreater surface-active efficiency than the corresponding esters ofsulphated straightchain monocarboxylic acids. This result is probablydue to the fact that a certain amount of branching increases thesolubility in water, improves the penetrating power and permits the useof high molecular weight products in a greater variety of commercialapplications. The beneficial effect of branching may be still furtherenhanced by employing a branched-chain alcohol as the esterifying agent.

In the preferred embodiment of the invention, the sulphate group isattached to a carbon atom, alpha, beta, gamma, or delta to the carboxylgroup of the ester. This preference is predicated on the fact that thecorresponding hydroxy branched-chain acids are more readily available'and on the indication that the sulphated products are more efiicient aswetting agents than those products which have the sulphate group furtherremoved from the carboxyl phation may be carried out in the presence of,solgroup. The markedly improved properties of the surface-active agentsof the present invention over older products such as sulphated castoroil are readily indicated by a comparison of the wetting efficiencies ofthese two types of products. Sulphated castor oil, which is derived froma straight chain acid and has the solubilizing groups 8 and 11 carbonsremoved from the carboxyl group, is greatly inferior as a wetting agentto the products of the present invention.

The water-soluble salts of the alkyl esters of branched-chain,aliphatic, sulphato-monocarboxylic acids are especially valuable assurfaceactive or capillary-active materials in that they have colloidalproperties and may therefore be advantageously used in any processinvolving wetting, penetrating, deterging, dispersing, emulsifying,frothing, foaming and kindred phenomena, and therefore they may beutilized in many of the technical applications of surface active agents.

The above description and examples are intended to be illustrative onlyand not to limit the scope of the invention. Any departure therefromwhich conforms to the spirit of the invention is intended to be includedwithin the scope of the appended claims.

I claim:

1. An alkyl ester of a branched-chain, aliphatic mono sulphatomonocarboxylic acid wherein the alkyl radical contains at least 4 carbonatoms and the monocarboxylic acid radical contains at least 4 carbonatoms.

2. An alkyl ester of a branched-chain, aliphatic alpha sulphatomonocarboxylic acid wherein the alkyl radical contains at least 4 carbonatoms and the monocarboxylic acid radical contains at least 4 carbonatoms.

3. An alkyl ester of a branched-chain, aliphatic mono sulphatomonocarboxylic acid wherein the alkyl radical is a branched, open chaincontaining at least 4 carbon atoms and the monocarboxylic acid radicalcontains at least 4 carbon atoms.

4. An alkyl ester of a branched-chain, aliphatic alpha sulphatomonocarboxylic acid wherein the alkyl radical contains from 6 to 16carbon atoms and the monocarboxylic'acid radical contains from 6 to 12carbon atoms.

5. An alkali metal salt of an alkyl ester of a branched-chain, aliphaticalpha-sulphato-monocarboxylic acid wherein the alkyl radical containsfrom 8 to 12 carbon atoms and the monocarboxylic acid radical containsfrom 7 to 9 carbon atoms.

'6. An alkali metal salt of an alkyl ester ofalpha-sulphato-beta-ethyl-valerate.

7. Octyl alpha-(sodium su1phato)-beta-ethyl valerate.

8. Dodecyl ethyl valerate.

9. An alkali metal salt of an alkyl ester of a branched-chain, aliphaticalpha-sulphato-monocarboxylic acid wherein the alkyl radical is abranched, open chain containing from 6 to 16 carbon atoms and themonocarboxylic acid radical contains from 6 to 12 carbon atoms.

10. Beta-ethylhexyl alpha-(sodium sulphato)- beta-ethylheptoate.

alpha- (sodium sulphato) -beta- JAIWES HERBERT WERNTZ.

